The present invention relates generally to packet communications systems, and more particularly to a congestion control method and apparatus for end-to-end packet communications.
In the past, such functions as error control and flow control between two communicating data terminal equipments are performed by switching nodes of a packet switched network. However, the recent tendency is toward allocating such control functions to data terminal equipments to perform end-to-end flow control and limiting the functions of the switched network only to data transfer to simplify protocols so that high speed packet transmission can be implemented for application to broadband ISDN (Integrated Services Digital Network). While this type of communication allows high speed exchanging of packets, difficulty will arise because of the end-to-end flow control mode to effect congestion control to prevent the system from becoming abnormally congested to an unmanageable level. To overcome this problem, two proposals have previously been made, one is to impose restrictions on the granting of permission to newly arising call connect requests from terminals and the other is to introduce a service class priority system by entering a priority indication to every packet and discard those packets having lower priority as discussed in a paper titled "Flow and Congestion Control for ISDN New Packet Mode Networks" by T. Y. Choi et al., submitted to the IEEE COMSOC International Workshop on Future Prospects of Burst/Packetized Multimedia Communications, Nov. 22-24, 1987, Osaka, Japan.
However, the proposed call restriction method has no restrictive effect on terminals which have already begun exchanging packets, and thus it takes a substantial amount of time before noticeable effect actually results. The proposed priority system is, on the other hand, likely to result in an additional transient increase in traffic due to possible end-to-end retransmission of packets before connection is cleared by timeout, and packetized speech and video signals tend to degrade in quality because no packet is returned for acknowledging correct receipt of these signals.